Apparatus for encasing magnetic cores



March 1, 1966 c. s. MUELLER APPARATUS FOR ENCASING MAGNETIC CORES FiledApril 13, 1964 FIG. 9.

FIG. 8.

FIG.

INVENTOR Charles S. Mueller ATTORNEYS United States Patent 3,238,481APPARATUS FGR ENCASING MAGNETIC CORES Charles S. Mueller, Philadelphia,Pa., assignor to Magnetic Metals Company, Camden, NJ. Filed Apr. 13,1964, Ser. No. 359,314 8 Claims. (Cl. 33692) This invention relates toapparatus for encasing mag netic cores in such a manner that dampingmaterials of the kind heretofore used are not required.

Magnetic cores are well known in the art and are used particularly inmagnetic amplifiers, saturable reactors and transformers, magneticrelays, etc. Commonly, such cores are of toroidal shape formed bywinding thin strips of magnetic material of varying thickness intotoroidal core form. The core may or may not have an air gap, nor is thepresent invention limited to cores having an annular configuration. Thecore is encased in a non-magnetic case which may be formed ofthermoplastics, thermosetting plastics, or a non-magnetic metal such asaluminum. The general practice is to construct the core and itsenclosure in such a way that there is clearance between the core and thewalls of the casing, thereby permitting expansion and contraction of thecore without binding the latter since it is important to avoidintroducing strains on the cores because of the deterioration ofmagnetic characteristics which may then occur.

It has been the practice in the prior art that before or after thetoroidal core of strip material is placed in its case, all the freespace remaining between the core and its enclosure be filled with adamping material such as silicone rubber, fluid, grease, or oil, beforefinally sealing the casing. It has heretofore been considered essentialthat such damping material be used to avoid rattling of the core in itscasing and to avoid strains on the core resulting from distortions ofthe casing since all such effects have been found to result in adverseeffects upon the cores magnetic properties.

It will readily be appreciated by one skilled in the art that there area number of problems associated with the use of a damping compound suchas the silicone fluids, greases, rubber, or oils referred to previously.First of all, such compounds are quite expensive, and this in itselfnecessarily raises the cost of each core. Another factor is theincreased labor costs in manufacturing cores resulting from thenecessity of filling each casing with the lamping medium after the corehas been inserted. in addition, it frequently happens that some of thedamping medium inadvertently gets onto the outside of the case, and thenadditional labor is involved in removing such material.

Described briefly, the present invention comprises an improved casingwhich makes it possible to dispose entirely of the use of dampingcompounds in the manufac ture of magnetic cores. The improved casing ofone embodiment of this invention includes, in part, a toroidalreceptacle which forms a part of the casing and has a U-shaped radialcross-section to receive the core, but with the bottom surface thereofhaving a plurality of permanently deformable, resilient, or frangibleupstanding elements which support the core upon its insertion and arepermanently deformed upon the application of pressure by the core onsuch elements, whereupon a permanent deformation takes place having theexact configuration of the core bottom so as to prevent its lateralshift- "ice ing when the casing is sealed. Various constructions andmodifications of the present invention are illustrated, includingparticularly one form in which both upper and lower portions of saidcasing have such upstanding deformable elements so that both havecore-receiving cavities formed therein when the two portions are tightlybrought together with the core inplace. Incidentally, it is recognizedthat this results in the application of some stresses on the top andbottom surfaces of the core itself, but these are minimal because of thepermanently deformable or frangible nature of the upstanding elements,and, furthermore, because the construction prevents the application ofany stresses to the sides of the magnetic core.

Considered more generally, the present invention relates to an encasedmagnetic core which comprises an encasement for receiving the core witha clearance between the inner side wall of the encasement and the outerwall of the core, together with means for preventing vibration of thecore within the encasement, this latter means comprising permanentlydeformable upstanding elements on at least the bottom wall of theencasement together with enclosure means for the encasement which isadapted to exert pressure on the core on its one surface so as to pressits opposite surface against the deformable means, whereby a recess isformed in the deformable means that tightly holds the core in place andprevents lateral shifting and vibration within the encasement.

It is, accordingly, an object of this invention to provide encasedmagnetic cores to construed that no damping fluids are required.

It is another object of this invention to provide an encasement formagnetic cores having frangible support means for the core in the bottomof the case which become permanently deformed when the core is placed inthe case so as to hold the core immovably therein.

It is a further object of this invention to provide a plastic case ofmagnetic cores having upstanding frangible rib members in the bottom ofat least one portion of the case which break away in part when a core isinserted therein and with pressure applied thereon, subsequent to whichthe core is relatively immovable laterally in said case.

Still another object of this invention is to provide a magnetic corecomprising a case containing a so-called spider or washer-type elementwhich can be inserted into the bottom of at least one portion of thecase, with the spider having upstanding, frangible rib members forsupporting the core when placed therein but with the up standing ribmembers being frangible or permanently deformable so as to automaticallyform therein a cavity for receiving the core when the latter is placedwith pressure on said spider, so that said spider will thereafterimmovably hold said core in place within its encasement.

Other objects, purposes, and characteristic features of the inventionwill be in part obvious from the accompanying drawing and in partpointed out as the description of the invention progresses.

In describing this invention, reference will be made to the accompanyingdrawings in which:

FIGURE 1 is an exploded view showing a magnetic core of the presentinvention including its case, with the upper and lower portions thereofseparated and also showing the toroidal magnetic core;

FIGURE 2 is a plan view of the upper half portion of the case.

FIGURE 3 is a cross-sectional view of a portion of the upper caseportion of FIGURE 2 taken along the line 3-3 of FIGURE 2;

FIGURE 4 is a plan View of the lower half portion of the case shown inFIGURE 1;

FIGURE 5 is a cross-sectional view of the lower case portion of FIGURE 4taken along the lines 5-5 of FIG- URE 4;

FIGURE 6 is a cross-sectional view showing the upper and lower caseportions in juxtaposition and with the inner magnetic core in place butwith the two half case portions separated a slight amount;

FIGURE 6A is a view similar to that of FIGURE 6 but showing the two caseportions brought tightly together under pressure;

FIGURE 7 is a cross-sectional view taken along the line 77 of FIGURE 4;and

FIGURES 8, 9 and 10 illustrate alternative embodiments of the presentinvention.

Referring to FIGURE 1, the exploded view shown there illustrates abottom toroidal casing member 10 which may be formed of a thermosettinggeneral purpose phenolic material, such as Bakelite, a tape-wound core11 of magnetic material, and an upper casing member 12 which isgenerally similar to the member 10 and may also be formed of the samematerial as member 10. FIGURE 1 shows that the member 10 has on itsinner bottom surface a plurality of integral upstanding ridges 13 whichare generally radial in nature and are spaced at substantially equalintervals about the bottom of the inside surface 10a of the member 10 soas to provide a support for the magnetic tape-wound core 11 when it isinserted within the casing 10. When the members 10 and 12 are formed ofa phenolic material as previously mentioned, it is then preferable thatthe member 12 also have the upstanding members or ribs on its innersurface in a manner analogous to that shown for the toroidal member 10.Such upstanding ribs are, of course, not evident in FIGURE 1 since itshows only the upper smooth surface of this particular member.

FIGURES 2 and 4 illustrate the fact that both these members 10 and 12may have the integral upstanding ribs disposed substantiallyequidistantly and radially about their bottom inner surfaces; thisFIGURE 2 shows the upper casing member 12 as having upstanding ridges13a, and FIGURE 4 shows the lower casing member 10 with its similarupstanding ridges 13. Although siX such ribs are shown in both FIGURES 2and 4, it is evident that proper support for the tape-wound core member11 shown in FIGURE 1 could also be provided by having as few as threesuch radial ribs. Of course, more than six such ribs can also beprovided and such modification is also within the scope of thisinvention.

FIGURES 3 and 5, respectively, comprise cross-sectional views of theouter toroidal portions of the members 12 and 10. The ribs 13 and 13aare shown with respect to each of the members 10 and 12. FIGURE 7 is acrosssectional view taken along the line 7-7 of FIGURE 4 andparticularly illustrates in cross-section one of the upstanding ribs 13,showing it to be generally knife-edged so that the knife-edge can bebroken away when the material is of a frangible nature such as thephenolic material mentioned previously, and when force is applied to theknife-edge by the core bottom. As illustrated in FIG- URE 7, it has beenfound in practice that a rib constructed to have an angle ofapproximately 20 works very satisfactorily when the material used is ageneral purpose phenolic. If the rib has too great an angle, it is toostiff and will not readily break off at its top, knife-edged portionwhen pressure is exerted thereon by the bottom surface of magnetic core11. On the other hand, if the angle is too small, the ridge breaks oflftoo readily and may break off substantially entirely when pressure isexerted thereon by core 11 or may break off during tumbling of theplastic parts which is often resorted to when Cir the individual partsare made by compression molding. With respect to the height of the rib13 above the bottom surface 19, it has been found that when a generalpurpose phenolic material is used, a height in the order of .02 of aninch is desirable. Of course, the dimensions given here are those whichhave been found to be satisfactory when the encasement is formed of ageneral purpose phenolic, but it will be understood that differentdimensions may be required when other types of materials are employed.

FIGURES 3 and 5 also illustrate how the two portions 11 and 12 of theencasement may be constructed so that they tend to interlock whenassembled. Thus, the depending circumferential shoulder 29 on member 12is adapted to abut ledge 30 on member 10; similarly, the circumferentialshoulder 27 on member 12 is adapted to abut ledge 28. In addition,shoulder 27 is provided with a slight rounded projection 15 on its innerside which is adapted to snap into a corresponding indentation 16 onledge 23 when the members 10 and 12 are brought fully together. However,it has been found that successful encased magnetic cores can be madewhich do not employ the interlocking means thus illustrated but merelyrely upon the close tolerances provided between the inner diameter at 17on member 12 and the outer diameter at 18 on member 10 so that when thetwo halves of the encasement 10 and 12 are assembled, frictional forceshold them tightly together.

FIGURE 6 illustrates one step in the operation of assembling thecomplete core and FIGURE 6A illustrates the completion of the assemblyoperation. FIGURE 6 illustrates the fact that the parts 10 and 12 are sodimensioned, particularly with respect to the combined depths of theirtoroidal U-shaped portions relative to the height of the core member 10itself, that when the core is inserted and the two members 10 and 12 arebrought together, with ribs 13 and 13a respectively contacting thebottom and top of core 11, there is a slight gap A between the opposingsurfaces of the members 10 and 12, e.g. between shoulder 27 and ledge28. This is done in order that the act of pressing the two membersclosely together will result in a crumbling of the frangible ribs inthose portions thereof where the core 11 is in contact with any ribportion. In other words, the act of forcing the two members 11) and 12together permanently deforms the ribs, thereby providing a recess ineach such rib for receiving the core and for holding the tape-wound coremember 11 tightly in place so that it cannot laterally shift within thespace provided. Thus, in FIGURE 6A, it will be noted that a rib 13 isbroken away wherever it lies opposite the upper edge of the tape-woundcore member 10 but is not broken away at those portions 21 and 22 sothat, in effect, each such rib 13 now is formed with a channel which isprecisely dimensioned in accordance with the radial thickness of thetape-Wound core member 11 so as to hold it without play or vibration inthe corresponding casing half 11} or 12. Incidentally, it has been foundthat a tape-wound core 11 is especially effective in breaking off aportion of each of the frangible ribs 13 and 13a since each laminationacts as a cutting edge relative to .the several ribs.

It will be appreciated that the concepts of this invention are in no waylimited to the use of plastic casing members 10 and 12. Thus, if thematerial of which the members 10 and 12 are fabricated is of a type suchas aluminum, which may render itself unsuitable for the production ofupstanding knife-edged ribs which are of a deformable or frangiblenature, it is readily possible to construct an insert for one of themembers 111 or 12 in the manner shown in FIGURE 8. Such an insert 23 maybe formed of a plastic or other suitable material having formed thereona plurality of upstanding knife-edged ribs 24 which again are formed ofa deformable or frangible material which may either take a permanentdeformation upon application of a force thereto by the bottom surface ofthe tape-wound core or may be of a frangible nature such that themembers 24 tend to crumble when force is applied thereto, againproviding a cavity or recess in which a tape-wound core 11 may fit andbe tightly held in place.

It is also possible to place one of the members 23 of FIGURE 8 in boththe upper and lower casing members 10 and 12 prior to insertion of thetape-wound core 10 although this is ordinarily not necessary and may beundesirable since the use of a washer 23 as a separate element in placeof the integral ribs shown, for example, in FIGURE 7, takes upadditional space within the casing member. Thus, it is generallypreferable to use only one such member 23 which is inserted into themember 10 immediately prior to the insertion of the tape-wound coremember 11 into the annular recess in member 10 on top of the washerelement 23.

FIGURE 9 illustrates an alternative embodiment of the invention whichmay be applied either to the construction of FIGURES 1-7 or may beapplied to a separate washer element such as element 23 of FIGURE 8. InFIGURE 9, instead of employing radial knife-edged ribs to support thecore, a plurality of concentric or spiral upstanding ridges are formed,but it is understood that the height and the angle of the ridges thusformed must be such that a permanent deformation or crumbling of thematerial will take place when the tape-wound core is inserted andpressure applied thereon in order that a cavity will be formed havingthe precise dimensions of the particular tape-wound core inserted so asto hold it tightly in place.

FIGURE 10 illustrates another alternative embodiment of the inventionwhich may be applied either to the construction of FIGURES 17 or mayalso be applied to a separate washer element comparable to the washerelement 23 of FIGURE 8. In FIGURE 10, the bottom surface 32, whethercorresponding to the bottom surface 10a of element 10 or correspondingto the surface 23 of the washer-type element of FIGURE 8, is providedwith a plurality of upstanding individual projections 26. Preferably,these projections extend around the circumference of the element andeach is formed with a height and cross-section which permits it to bereadily deformed or broken off at its topmost portion when pressure isexerted thereon by the core 11. Consequently, those projections 26 whichare broken off or deformed provide a recess for receiving the core 11,whereas those projections which are not broken off provide means whichare effective to exert forces against the sides of the core 11 toprevent its lateral shifting or vibration within the encasement.

It is to be further understood that the invention is in no way intendedto be limited to the general type of construction shown in FIGURE 1wherein two generally similar toroidal-shaped mating members, whenfitted together, form the encasement for the magnetic core, but that theinvention applies equally well to other known constructions includingthose wherein a magnetic core fits entirely within an annulartrough-shaped member, with a generally fiat lid or comparable sealingmeans providing the enclosure for the encasement. It will be readilyunderstood by one skilled in the art and with reference to thedisclosure herein, that the principles of this invention wherein apermanently deformable means is employed may equally Well be used withother such constructions.

Having described a preferred embodiment of my invention and in additionseveral alternative embodiment-s, I desire it .to be understood thatvarious modifications and alternations may be made to the specific formshown without in any manner departing from the scope of my invention.

What I claim is:

I. An encased magnetic core comprising, a casing of non-magneticmaterial having walls forming a toroidal container which is generallyU-shaped in radial section, a

toroidal magnetic core within said container with a clearance betweenthe inner walls of said container and the outer walls of said magneticcore, means on the inner bottom wall of said U-shaped toroidal containersupporting the bottom surface of said core, said supporting means beingfrangible so as to fracture readily under pressure and define a recesstherein upon the application of pressure thereon by said core whichrecess substantially conforms to the shape of the contacting bottomsurface of said core, said recess together with that port-ion of saidsupporting means which is not deformed by said core bottom prohibitinglateral movement of said core within said casing, and enclosure meansfor said casing tightly contacting the upper surface of said core topress said core tightly against said supporting means at the bottom ofsaid toroidal chamber.

2. The invention as defined in claim 1 wherein said supporting meanscomprises at least three radially extending upstanding ridges integralwith said inner bottom wall of said container; said ridges beingknife-edged in crosssection with the narrow portion thereof extendingupwardly toward the contacting surface of said core.

3. The invention as defined in claim 2 wherein each said ridge forms anacute angle of about 20 and extends approximately .02 of an inch abovesaid inner bottom wall of said container.

4. The invention as defined in claim 1 wherein said supporting meanscomprises a separate washer-shaped element resting upon said innerbottom wall of said container, said separate element having a pluralityof upstanding frangible elements on that face thereof which contactssaid core bottom, said frangible elements readily fracturing to formsaid recess when said core is pressed tightly thereagainst.

5. The invention as defined in claim 1 wherein said supporting meanscomprises generally circular and substantially concentric upstandingknife-edged ridges integral with the bottom surface of said toroidalcore-receiving chamber.

6. The invention as defined in claim 1 wherein said enclosure means alsoincludes frangible means on its inner surface which contacts the uppersurface of said core to thereby also form a recess therein substantiallyconforming to the contours of the upper surface of said core so as toaid in preventing lateral displacement of said core within said casing.

7. The invention as defined in claim 1 wherein said supporting meanscomprises a plurality of discrete pointed projections extending upwardlyfrom said inner bottom wall of said toroidal chamber, whereby certain ofsaid projections are permanently deformed by said core when said core ispressed tightly against said inner bottom wall, and the remainderthereof which are not so permanently deformed exert pressures on thesides of the said core to prohibit lateral displacement thereof withinsaid casing.

8. In combination, a magnetic core, a casing for said magnetic corecomprising, two separate mateable members, one of said members having aninner bottom wall and opposing inner side walls forming a chamberreceiving said magnetic core with clearance between the inner side wallsand the corresponding surfaces of the magnetic core, the other of saidmembers having an inner top wall to oppose said inner bottom wall whensaid members are mated with spacing therebetween when said member arefully mated which at least equals the corresponding dimension of saidmagnetic core, a plurality of upstanding frangible elements projectingoutwardly from at least one of said inner top and bottom walls to formtop and bottom core abutting surfaces whose spacing is less than thecorresponding dimension of said core, whereby upon the exertion of forceupon said mateable members forcing said members together into fullmating position at least a portion of said upstanding frangible elementsare permanently deformed to form a recess for the magnetic core forpreventing lateral motion of the magnetic core within said casing.

References Cited by the Examiner UNITED STATES PATENTS 2,198,803 4/1940Carlson et al. 336-92 X 2,641,743 6/1953 Bonanno 33692 X 2,947,4598/1960 Pregent 20646 2,988,715 6/1961 Gizyanski et a1 336-92 8 3,014,97812/1961 LeBert et a1 174--52.5 3,018,455 1/1962 Brandon et a1. 336-100FOREIGN PATENTS 2,901 3/1894 Great Britain.

ROBERT K. SCHAEFER, Primary Examiner.

JOHN F. BURNS, Examiner.

D. J. BADER, Assistant Examiner.

1. AN ENCASED MAGNETIC CORE COMPRISING, A CASING OF NON-MAGNETICMATERIAL HAVING WALLS FORMING A TOROIDAL CONTAINER WHICH IS GENERALLYU-SHAPED IN RADIAL SECTION, A TOROIDAL MAGNETIC CORE WITHIN SAIDCONTAINER WITH A CLEARANCE BETWEEN THE INNER WALLS OF SAID CONTAINER ANDTHE OUTER WALLS OF SAID MAGNETIC CORE, MEANS ON THE INNER BOTTOM WALL OFSAID U-SHAPED TOROIDAL CONTAINER SUPPORTING THE BOTTOM SURFACE OF SAIDCORE, SAID SUPPORTING MEANS BEING FRANGIBLE SO AS TO FRACTURE READILYUNDER PRESSURE AND DEFINE A RECESS THEREIN UPON THE APPLICATION OFPRESSURE THEREON BY SAID CORE WHICH RECESS SUBSTANTALLY CONFORMS TO THESHAPE OF THE CONTACTING BOTTOM SURFACE OF SAID CORE, SAID RECESSTOGETHER WITH THAT PORTION OF SAID SUPPORTING MEANS WHICH IS NOTDEFORMED BY SAID CORE BOTTOM PROHIBITING LATERAL MOVEMENET OF SAID COREWITHIN SAID CASING AND ENCLOSURE MEANS FOR SAID CASING TIGHTLYCONTACTING THE UPPER SURFACE OF SAID CORE TO PRESS SAID CORE TIGHTLYAGAINST SAID SUPPORTING MEANS AT THE BOTTOM OF SAID TOROIDAL CHAMBER.